NASA Facts National Aeronautics and Space Administration

Dryden Flight Research Center P.O. Box 273 Edwards, California 93523 Voice 661-276-3449 FAX 661-276-3566 [email protected] FS-1994-11-035 DFRC D-558-II

D-558-II Skyrocket being launched from a P2B.

The Douglas D-558-II "Skyrockets" were among the early transonic research airplanes like the X-1, X-4, X-5, and X-92A. Three of the single-seat, swept-wing aircraft flew from 1948 to 1956 in a joint program involving the National Advisory Committee for Aeronautics (NACA), with its flight research done at the NACA's Muroc Flight Test Unit in Calif., redesignated in 1949 the High-Speed Flight Research Station (HSFRS); the Navy- Marine Corps; and the Douglas Aircraft Co. The HSFRS is now known as the NASA Dryden Flight Research Center. The Skyrocket made aviation history when it became the first airplane to fly twice the speed of sound.

The II in the aircraft's designation referred to the fact that the Skyrocket was the phase-two version of what had originally been conceived as a three-phase program, with the phase-one aircraft having straight wings. The third

1 phase, which never came to fruition, would have powered aircraft and funded the X-1, while the NACA involved constructing a mock-up of a combat-type and Navy preferred a more conservative design and aircraft embodying the results from the testing of the pursued the D-558, with the NACA also supporting phase one and two aircraft. the X-1 research.

Douglas pilot John F. Martin made the first flight at The Navy contracted with Douglas to design the Muroc Army Airfield (later renamed Edwards Air airplane, and in the course of the design process, the Force Base) in Calif. on February 4, 1948. The goals D-558 came to be divided into two separate phases, of the program were to investigate the characteristics with phase one being a straight-wing turbojet aircraft of swept-wing aircraft at transonic and supersonic and phase two consisting of a swept-wing design with speeds with particular attention to pitch-up turbojet and rocket propulsion. At the NACA's sug- (uncommanded rotation of the nose of the airplane gestion, based on the research of Robert Jones at upwards)--a problem prevalent in high-speed service Langley and captured German documents, Douglas aircraft of that era, particularly at low speeds during and the Navy had agreed to the swept-wing design, take-off and landing and in tight turns. and to provide sufficient power to propel the swept- wing airplane past Mach 1, they also agreed to add The three aircraft gathered a great deal of data about rocket propulsion. pitch-up and the coupling of lateral (yaw) and longitu- dinal (pitch) motions; wing and tail loads, lift, drag, Then, to fit both a turbojet and rocket engine in the and buffeting characteristics of swept-wing aircraft at phase two aircraft required a new fuselage. Like the transonic and supersonic speeds; and the effects of the D-558-I, the Skyrocket featured a horizontal stabilizer rocket exhaust plume on lateral dynamic stability high on the vertical tail to avoid the wake from the throughout the speed range. (Plume effects were a wing. As with the X-1 and the D-558-1, the Skyrocket new experience for aircraft.) The number three air- also featured, at NACA suggestion, a horizontal craft also gathered information about the effects of stabilizer that was thinner than the wing and movable external stores (bomb shapes, drop tanks) upon the in flight so as to avoid simultaneous shock wave aircraft's behavior in the transonic region (roughly 0.7 effects for the wing and horizontal tail and to provide to 1.3 times the speed of sound). pitch (nose up or down) control when shock waves made the elevators ineffective. While Douglas was In correlation with data from other early transonic constructing the D-558-IIs, the NACA continued to research aircraft such as the XF-92A, this information furnish the contractor data it needed on aircraft perfor- contributed to solutions to the pitch-up problem in mance based on tests in Langley wind tunnels and swept-wing aircraft. with rocket-propelled models from the Wallops Island Pilotless Aircraft Research Station. Design Program History The need for transonic research airplanes grew out of two conditions that existed in the early 1940s. One The three airplanes flew a total of 313 times--123 by was the absence of accurate wind tunnel data for the the number one aircraft (Bureau No. 37973--NACA speed range from roughly Mach 0.8 to 1.2. The other was the fact that fighter aircraft like the P-38 "Light- ning" were approaching these speeds in dives and breaking apart from the effects of compressibility-- increased density and disturbed airflow as the speed approached that of sound, creating shock waves. People in the aeronautics community--especially the NACA, the Army Air Forces (AAF), and the Navy-- agreed on the need for a research airplane with enough structural strength to withstand compressibility effects in the transonic region. The AAF preferred a rocket- D-558-II Skyrocket on the Lakebed at Edwards AFB. 2 143), 103 by the second Skyrocket (Bureau No. The NACA engineers studied the behavior of the 37974--NACA 144), and 87 by airplane number three aircraft before beginning their own flight research in (Bureau No. 37975--NACA 145). Skyrocket 143 flew the airplane in September 1951. Over the next couple all but one of its missions as part of the Douglas of years, NACA pilot A. Scott Crossfield flew the contractor program to test the airplane's performance. airplane 20 times to gather data on longitudinal and lateral stability and control, wing and tail loads, and NACA aircraft 143 was initially powered by a lift, drag, and buffeting characteristics at speeds up to Westinghouse J-34-40 turbojet engine configured only Mach 1.878. for ground take-offs, but in 1954-55 the contractor modified it to an all-rocket air-launch capability At that point, Marine Lt. Col. Marion Carl flew the featuring an LR8-RM-6, 4-chamber Reaction Motors airplane to a new (unofficial) altitude record of 83,235 engine rated at 6,000 pounds of thrust at sea level (the feet on August 21, 1953, and to a maximum speed of Navy designation for the Air Force's LR-11 used in Mach 1.728. the X-1). In this configuration, NACA research pilot John McKay flew the airplane only once for familiar- Following Carl's completion of these flights for the ization on September 17, 1956. The 123 flights of Navy, NACA technicians at the High-Speed Flight NACA 143 served to validate wind-tunnel predictions Research Station (HSFRS) near Mojave, Calif., outfit- of the airplane's performance, except for the fact that ted the LR-8 engine's cylinders with nozzle extensions the airplane experienced less drag above Mach 0.85 to prevent the exhaust gas from affecting the rudders than the wind tunnels had indicated. at supersonic speeds. This addition also increased the engine's thrust by 6.5 percent at Mach 1.7 and 70,000 NACA 144 also began its flight program with a feet. turbojet powerplant. NACA pilots Robert A. Champine and John H. Griffith flew 21 times in this Even before Marion Carl had flown the Skyrocket, configuration to test airspeed calibrations and to HSFRS Chief Walter C. Williams had petitioned research longitudinal and lateral stability and control. In the process, during August of 1949 they encoun- tered pitch-up problems, which NACA engineers recognized as serious because they could produce a limiting and dangerous restriction on flight perfor- mance. Hence, they determined to make a complete investigation of the problem.

In 1950, Douglas replaced the turbojet with an LR-8 rocket engine, and its pilot, William B. Bridgeman, flew the aircraft seven times up to a speed of Mach 1.88 (1.88 times the speed of sound) and an altitude of Graphic showing the D-558-II Wing Configurations. 79,494 feet (the latter an unofficial world's altitude record at the time, achieved on August 15, 1951). In the rocket configuration, a Navy P2B (Navy version of NACA headquarters unsuccessfully to fly the aircraft the B-29) launched the airplane at approximately to Mach 2 to garner the research data at that speed. 30,000 feet after taking off from the ground with the Finally, after Crossfield had secured the agreement of Skyrocket attached beneath its bomb bay. During the Navy's Bureau of Aeronautics, NACA director Bridgeman's supersonic flights, he encountered a Hugh L. Dryden relaxed the organization's usual violent rolling motion known as lateral instability that practice of leaving record setting to others and con- was less pronounced on the Mach 1.88 flight on sented to attempting a flight to Mach 2. August 7, 1951, than on a Mach 1.85 flight in June when he pushed over to a low angle of attack (angle of In addition to adding the nozzle extensions, the NACA the fuselage or wing to the prevailing wind direction). flight team at the HSFRS chilled the fuel (alcohol) so

3 more could be poured into the tank and waxed the wind-tunnel test results with actual flight values, fuselage to reduce drag. With these preparations and enhancing the abilities of designers to produce more employing a flight plan devised by project engineer capable aircraft for the armed services, especially Herman O. Ankenbruck to fly to approximately those with swept wings. Moreover, data on such 72,000 feet and push over into a slight dive, Crossfield matters as stability and control from this and other made aviation history on November 20, 1953, when he early research airplanes aided in the design of the flew to Mach 2.005 (1,291 miles per hour). He be- century series of fighter airplanes, all of which fea- came the first pilot to reach Mach 2 in this, the only tured the movable horizontal stabilizers first employed flight in which the Skyrocket flew that fast. on the X-1 and D-558 series.

Following this flight, Crossfield and NACA pilots The Aircraft Joseph A. Walker and John B. McKay flew the air- plane for such purposes as to gather data on pressure All three of the Skyrockets had a height of 12 feet 8 distribution, structural loads, and structural heating, inches, a length of 42 feet, and 35-degree swept wings with the last flight in the program occurring on De- cember 20, 1956, when McKay obtained dynamic stability data and sound-pressure levels at transonic speeds and above.

Meanwhile, NACA 145 had completed 21 contractor flights by Douglas pilots Eugene F. May and Bill Bridgeman in November 1950. In this jet-and-rocket- propelled craft, Scott Crossfield and Walter Jones began the NACA's investigation of pitch-up lasting from September 1951 well into the summer of 1953. They flew the Skyrocket with a variety of wing-fence, wing-slat, and leading-edge chord extension configu- rations, performing various maneuvers as well as straight-and-level flying at transonic speeds. While fences significantly aided recovery from pitch-up conditions, leading edge chord extensions did not, D-558-II 3-Dimentional Drawing disproving wind-tunnel tests to the contrary. Slats (long, narrow auxiliary airfoils) in the fully open position eliminated pitch-up except in the speed range with a span of 25 feet. around Mach 0.8 to 0.85. Until configured for air launch, NACA 143 featured a In June 1954, Crossfield began an investigation of the Westinghouse J-34-40 turbojet engine rated at 3,000 effects of external stores (bomb shapes and fuel tanks) pounds of static thrust. It carried 260 gallons of upon the aircraft's transonic behavior. McKay and aviation gasoline and weighed 10,572 pounds at take- Stanley Butchart completed the NACA's investigation off. of this issue, with McKay flying the final mission on August 28, 1956. NACA 144 (and NACA 143 after modification in 1955) was powered by an LR-8-RM-6 rocket engine Besides setting several records, the Skyrocket pilots rated at 6,000 pounds of static thrust. Its propellants had gathered important data and understanding about were 345 gallons of liquid oxygen and 378 gallons of what would and would not work to provide stable, diluted ethyl alcohol. In its launch configuration, it controlled flight of a swept-wing aircraft in the tran- weighed 15,787 pounds. sonic and supersonic flight regimes. The data they gathered also helped to enable a better correlation of NACA 145 had both an LR-8-RM-5 rocket engine

4 rated at 6,000 pounds of static thrust and featured a For Further Reading Westinghouse J-34-40 turbojet engine rated at 3,000 pounds of static thrust. It carried 170 gallons of liquid The best single source on the Skyrocket is Richard P. oxygen, 192 gallons of diluted ethyl alcohol, and 260 Hallion's Supersonic Flight: Breaking the Sound gallons of aviation gasoline for a launch weight of Barrier and Beyond, The Story of the Bell X-1 and 15,266 pounds. Douglas D-558 (revised edn.; London and Washing- ton, 1997). One of the Skyrocket pilots, A. Scott NACA 143 is currently in storage at the Planes of Crossfield (with Clay Blair, Jr.), has told about his Fame Museum, Ontario, California. The second own flying career in Always Another Dawn: The Story Skyrocket, NACA 144, is in the Smithsonian of a Rocket Test Pilot (Cleveland, 1960). Another Institution's National Air and Space Museum in Skyrocket pilot, William Bridgeman, has related his Washington, D.C. NACA 145 is on display in front of experiences in a book written with Jacqueline Hazard, the Antelope Valley College in Lancaster, California. The Lonely Sky (New York, 1955).

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